grsecurity is a set of patches for the Linux kernel which emphasize security enhancements.[2] The patches are typically used by computer systems which accept remote connections from untrusted locations, such as web servers and systems offering shell access to its users. Grsecurity provides a collection of security features to the Linux kernel, including address space protection, enhanced auditing and process control. Work on grsecurity began in February 2001 as a port of Openwall Project's security-enhancing patches for version 2.4 of the Linux kernel mainline. The first release of grsecurity was for the Linux kernel 2.4.1.[citation needed]

Contents

Since September 9, 2015, the availability of stable grsecurity patches has become limited to the commercial customers of grsecurity. The testing versions of grsecurity patches, as well as the source code and patches for related userspace utilities, remain publicly available.[3][4][5]

A major component bundled with grsecurity is PaX. Among other features, the patch flags data memory, the stack, for example, as non-executable and program memory as non-writable. The aim is to prevent memory from being overwritten, which can help to prevent many types of security vulnerabilities, such as buffer overflows. PaX also provides address space layout randomization (ASLR), which randomizes important memory addresses to reduce the probability of attacks that rely on easily predicted memory addresses. PaX is not developed by the grsecurity developers. It is available in other Linux distributions such as Gentoo or IPFire, and directly from grsecurity.[6]

Another notable component of grsecurity is that it provides a full role-based access control (RBAC) system. RBAC is intended to restrict access to the system further than what is normally provided by Unixaccess control lists, with the aim of creating a fully least-privilege system, where users and processes have the absolute minimum privileges to work correctly and nothing more. This way, if the system is compromised, the ability of the attacker to damage or gain sensitive information on the system can be drastically reduced. RBAC works through a collection of roles. Each role can have individual restrictions on what it can or cannot do, and these roles and restrictions form an access policy which can be amended as needed.

Among other things, it can be configured to audit a specific group of users, mounting/unmounting of devices, changes to the system time and date, and chdir logging. Some of the other audit types allow the administrator to also log denied resource attempts, failed fork attempts, IPC creation and removal, and exec logging together with its arguments.

Trusted path execution is another optional feature that can be used to prevent users from executing binaries not owned by the root user, or world-writable binaries. This is useful to prevent users from executing their own malicious binaries or accidentally executing world-writable system binaries that could have been modified by a malicious user.

grsecurity also hardens the way chroot "jails" work. A chroot jail can be used to isolate a particular process from the rest of the system, which can be used to minimise the potential for damage should the service be compromised. There are ways to "break out" of a chroot jail, which grsecurity attempts to prevent.

There are also other features that increase security and prevent users from gaining unnecessary knowledge about the system, such as restricting the dmesg and netstat commands to the root user.[7]